SGK1 inhibits cellular apoptosis and promotes proliferation via the MEK/ERK/p53 pathway in colitis

AIM: To investigate the role of serum-and-glucocorticoid-inducible-kinase-1(SGK1) in colitis and its potential pathological mechanisms.METHODS: SGK1 expression in mucosal biopsies from patients with active Crohn's disease(CD) and normal controls was detected by immunohistochemistry. We established an acute colitis model in mice induced by 2,4,6-trinitrobenzene sulfonicacid, and demonstrated the presence of colitis using the disease activity index, the histologic activity index and hematoxylin and eosin staining. The cellular events and potential mechanisms were implemented with small interference RNA and an inhibitor of signaling molecule(i.e., U0126) in intestinal epithelial cells(IECs). The interaction between SGK1 and the signaling molecule was assessed by coimmunoprecipitation.RESULTS: SGK1 expression was significantly increased in the inflamed epithelia of patients with active CD and TNBS-induced colitis model(0.58 ± 0.055 vs 0.85 ± 0.06, P < 0.01). At the cellular level, silencing of SGK1 by small interference RNA(si SGK1) significantly inhibited the phosphorylation of mitogen-activated protein kinase kinase 1(MEK1) and the downstream molecule extracellular signal regulated protein kinase(ERK) 1/2, which induced the upregulation of p53 and Bcl-2-associated X protein, mediating the subsequent cellular apoptosis and proliferation in IECs. Cells treated with MEK1 inhibitor(i.e., U0126) before si SGK1 transfection showed a reversal of the si SGK1-induced cellular apoptosis. CONCLUSION: Our data suggested that SGK1 may protect IECs in colitis from tumor necrosis factor-α-induced apoptosis partly by triggering MEK/ERK activation.

Incomplete reproductive isolation between Rhododendron taxa enables hybrid formation and persistence

The evolutionary consequences of hybridization ultimately depend on the magnitude of reproductive isolation between hybrids and their parents. We evaluated the relative contributions of pre-and post-zygotic barriers to reproduction for hybrid formation, hybrid persistence and potential for reproductive isolation of hybrids formed between two Rhododendron species,R. spiciferum and R. spinuliferum. Our study established that incomplete reproductive isolation promotes hybrid formation and persistence and delays hybrid speciation.All pre-zygotic barriers to reproduction leading to hybrid formation are incomplete: parental species have overlapping flowering; they share the same pollinators;reciprocal assessments of pollen tube germination and growth do not differ among parents. The absence of post-zygotic barriers between parental taxa indicates that the persistence of hybrids is likely. Reproductive isolation was incomplete between hybrids and parents in all cases studied, although asymmetric differences in reproductive fitness were prevalent and possibly explain the genetic structure of natural hybrid swarms where hybridization is known to be bidirectional but asymmetric. Introgression, rather than speciation, is a probable evolutionary outcome of hybridization between the two Rhododendron taxa. Our study provides insights into understanding the evolutionary implications of natural hybridization in woody plants.